Ezgi Sahin

Enhanced optical nonlinearities in CMOS-compatible ultra-silicon-rich nitride photonic crystal waveguides

We present the design, fabrication, and characterization of photonic crystal waveguides (PhCWs) on an ultra-silicon-rich nitride (USRN) platform, with the goal of augmenting the optical nonlinearities. The design goals are to achieve an optimized group index curve on the PhCW band edge with a non-membrane PhCW with symmetric SiO2 undercladding and overcladding, so as to maintain back-end CMOS compatibility and better structural robustness. Linear optical characterization, as well as nonlinear optical characterization of PhCWs on ultra-silicon-rich nitride is performed at the telecommunication wavelengths. USRNs negligible two-photon absorption and free carrier losses at the telecommunication wavelengths ensure that there is no scaling of two-photon related losses with the group index, thus maintaining a high nonlinear efficiency. Self-phase modulation experiments are performed using a 96.6u2009μm PhCW. A 1.5π phase shift is achieved with an input peak power of 2.5u2009W implying an effective nonlinear parameter ...

Large, scalable dispersion engineering using cladding-modulated Bragg gratings on a silicon chip

A cladding-modulated 1D photonic crystal is realized for creating ultra-large dispersion on a silicon chip. Both normal dispersion and anomalous dispersion are realized on the same waveguide device. The design, fabrication, and characterization of the devices are demonstrated. The device exploits adjacent pillars positioning to engineer the dispersion, as well as the variation of the distance between the pillar and waveguide to realize apodization. Devices achieving a group delay dispersion coefficient of −3.61 ps/nm and 3.28 ps/nm are demonstrated with a footprint of 1.27u2009×u20091.7u2009mm2. The demonstrated devices possess a group delay dispersion coefficientu2009×u2009bandwidth product as large as 72 ps on a silicon, CMOS-compatible chip.

Ultra-silicon-rich nitride devices for high nonlinear figure of merit optical signal processing

CMOS nonlinear platforms are desirable for their ease of integration with CMOS electronics and large-scale manufacturability. A continuum of CMOS materials spanning from silicon dioxide to amorphous silicon exist. We have developed ultra-silicon-rich nitride possesses a large linear and nonlinear refractive index while still maintaining a sufficiently large bandgap to preclude two photon absorption at the telecommunications wavelength. We discuss recent developments of nonlinear optical signal processing leveraging the ultra-silicon-rich nitride platform. Optical parametric gain of up to 42.5dB is demonstrated, as well as supercontinuum generation. Enhanced optical nonlinearity using photonic crystal waveguides is also demonstrated, with the slow light effect enabling a nonlinear parameter of 1.97 × 104 (Wm)−1.

Optimized optical devices for edge-coupling-enabled silicon photonics platform

We present a library of high-performance passive and active silicon photonic devices at the C-band that is specifically designed and optimized for edge-coupling-enabled silicon photonics platform. These devices meet the broadband (100 nm), low-loss (< 2dB per device), high speed (≥ 25 Gb/s), and polarization diversity requirements (TE and TM polarization extinction ratio ≤ 25 dB) for optical communication applications. Ultra-low loss edge couplers, broadband directional couplers, high-extinction ratio polarization beam splitters (PBSs), and high-speed modulators are some of the devices within our library. In particular, we have designed and fabricated inverse taper fiber-to-waveguide edge couplers of tip widths ranging from 120 nm to 200 nm, and we obtained a low coupling loss of 1.80±0.28 dB for 160 nm tip width. To achieve polarization diversity operation for inverse tapers, we have experimentally realized different designs of polarization beam splitters (PBS). Our optimized PBS has a measured extinction ratio of ≤ 25 dB for both the quasiTE modes, and quasi-TM modes. Additionally, a broadband (100 nm) directional coupler with a 50/50 power splitting ratio was experimentally realized on a small footprint of 20×3 μm2 . Last but not least, high-speed silicon modulators with a range of carrier doping concentrations and offset of the PN junction can be used to optimise the modulation efficiency, and insertion losses for operation at 25 GHz.

High gain optical parametric amplification in ultra-silicon-rich nitride (USRN) waveguides

Optical parametric amplifiers rely on the high Kerr nonlinearities and low two-photon absorption (TPA) to achieve large optical amplification. The high Kerr nonlinearity enables efficient energy transfer from the optical pump to the signal. On the other hand, the TPA process competes with the amplification process, and thus should be eliminated. Through Miller’s rule and Kramers-Kronig relations, it is known that the material’s Kerr nonlinearity scales inversely proportional to the band-gap, while the TPA process occurs when the photon energy is larger than the band-gap energy and Urbach tails, thus presenting a trade-off scenario. Based on these requirements, we have designed a CMOScompatible, band-gap engineered nitride platform with ultra-rich silicon content. The silicon nitride material is compositionally engineered to have a band-gap energy of 2.1 eV, which is low enough to confer a high Kerr nonlinearity, but still well above the energy required for the TPA process to occur. The new material, which we called ultra-silicon-rich nitride (USRN), has a material composition of Si7N3, a high Kerr nonlinearity of 2.8x10-13 cm2/W, and a negligible TPA coefficient. In optical amplification experiments, 500 fs pulses at 14 W peak power and centered around 1560 nm are combined with continuous wave signals. The maximum parametric gain of the signal could reach 42.5 dB, which is one of the largest gains demonstrated on CMOS platforms to date. Moreover, cascaded four-wave mixing down to the third idler, which was usually observed for mid-infrared silicon waveguides, is unprecedentedly observed at this spectrum.

Broadband silicon bridge waveguide polarization beam splitter

We have successfully fabricated and measured our silicon bridge waveguide polarization beam splitter (PBS). Our proposed PBS is based on a bend directional coupler with a bend bridge waveguide and is experimentally realized using silicon waveguide thickness of 220 nm and 250 nm, which are the commonly used silicon thickness for silicon photonics manufacturing. Our experimental results demonstrated high extinction ratio of > 20 dB for the TE-like mode, and > 15 dB for the TM-like mode across a broad bandwidth of 90 nm that covers the entire C-band with a small footprint of ~18×9 μm2. On-chip high performance PBS is important for polarization diversity in integrated photonics, and for communication applications such as dual-polarization quadrature phase-shift keying (DP-QPSK) modulation.

High-performance silicon-on-insulator polarization beam splitter using novel bend directional coupler

High performance silicon-on-insulator polarization beam splitter with a small footprint of ~18 × 9 μm2 is demonstrated using a bend directional coupler with a bridge waveguide. High extinction ratio of > ~20 dB over the entire C band is achieved for both TE-like and TM-like polarizations.